Active isolation module

ABSTRACT

A vibration isolator for isolating a load from a floor. The vibration isolator may have an active isolator assembly that isolates the load in a first direction and a passive isolator assembly that isolates the member in a second direction or directions. The active isolator assembly may include a single actuator that is coaxially aligned with a sensor. The sensor and actuator can be connected to a controller which together provide active isolation of the load. The passive isolator assembly may include a pendulum that is coupled to a dashpot. Providing a system with just one actuator significantly reduces the cost of the vibration isolator with respect to isolators of the prior art.

REFERENCE TO CROSS-RELATED APPLICATION

This application is a continuation of application Ser. No. 09/114,773,filed on Jul. 14, 1998, U.S. Pat. No. 6,209,841.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vibration isolator that can isolate aload such as a table platform from a surface such as a floor of abuilding.

2. Background Information

It is sometimes desirable to prevent relative movement between twosurfaces. For example, integrated circuit are typically fabricated on aplatform with photolithographic equipment. The location of directedlight used to align and fabricate the integrated circuit must be veryaccurate.

The table is typically placed on the floor of a clean room. The floormay undergo vibrational movement that can be transferred to the table.The vibration may cause a displacement of the table which reduces theaccuracy of the fabrication process.

Some tables incorporate vibration isolators to reduce or prevent thefloor vibration from being transferred to the table. U.S. Pat. No.5,000,415 issued to Sandercock and assigned to the assignee of thepresent invention, Newport Corp., discloses a vibration isolator thathas an active isolator assembly which actively isolates a load from afloor. The active isolator assembly includes a plurality ofpiezoelectric actuators which can vary the distance between the load andthe floor surface to compensate for movement in the floor. For example,the floor may oscillate so that the floor surface moves toward the loadand away from the load. When the floor moves toward the load thepiezoelectric actuators contract so that the motion of the load relativeto inertial space is reduced compared to that of the floor. Likewise,when the floor moves away from the load the actuators expand.

The active vibration isolator disclosed in the Sandercock patentincludes a sensor that senses the movement of the floor and circuitry toprovide a control loop to synchronize the contraction/expansion of theactuators with the movement in the floor. Sandercock also discloses theuse of sensors which sense the velocity of the load to provide afeedback loop that is coupled to the feedforward loop.

The piezoelectric actuators and control loops are capable of isolatingthe load for relatively low frequencies. To roll off high frequencies,Sandercock employs an elastomeric mount that is interposed between theload and the actuators. The elastomeric mount has a resonant frequencythat varies with the weight of the load. The variation in the resonantfrequency requires a calibration of the system during installation, or areconfiguration, to compensate for a different weight of the load. Itwould be desirable to provide an elastomeric mount which has a resonantfrequency that is relatively constant for a predetermined range of loadweights.

U.S. Pat. No. 5,660,255 issued to Schubert et al. discloses a vibrationisolator which has a number of piezoelectric actuators to isolate a loadin a vertical direction and additional piezoelectric actuators toisolate the load in a horizontal plane. The Schubert vibration isolatorprovides active isolation in both the vertical and horizontaldirections. The piezoelectric actuators are relatively expensive.Therefore providing additional horizontal actuators increases the costof assembling the vibration isolator. It would be desirable to haveeffective vibration isolators that can provide vertical and horizontalisolation, and which cost less to produce than isolators of the priorart.

Even with vibration isolation the load may move relative to the floor inthe horizontal plane. It may be desirable to move and adjust the load toan original reference position. It would therefore be desirable toprovide a docking system which can align and secure the load in areference position.

The drive signal which excites the piezoelectric actuator is typically afunction of a gain value and a transfer function which are either storedin a memory device of a controller that controls the system, or builtinto analog electronics that control the system. The stored transferfunction determines the transient response time and bandwidth of theisolator. Vibration isolators of the prior art do not allow the systemoperator to vary the transfer function and the resultant transientresponse time and bandwidth of the system. It would be desirable toprovide a vibration isolator which allows an operator to vary thetransfer function used to determine the drive signal of the actuator.

SUMMARY OF THE INVENTION

One embodiment of the present invention is a vibration isolator forisolating a load from a surface. The vibration isolator may have anactive isolator assembly that isolates the load in a first direction anda passive isolator assembly that isolates the load in a seconddirection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of a table assembly of thepresent invention;

FIG. 2 is a side view of a foot of the table assembly;

FIG. 3 is a cross-sectional view of an embodiment of a vibrationisolator of the table assembly;

FIG. 4 is a cross-sectional view of a damper assembly of the vibrationisolator;

FIG. 5 is a schematic of the isolator;

FIG. 6 is an electrical schematic of a controller that controls theisolator;

FIG. 7 is a flowchart showing a routine performed by a controller of theisolator.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of the present invention is a vibration isolator forisolating a load from a surface. The vibration isolator may have anactive isolator assembly that isolates the load in a first direction anda passive isolator assembly that isolates the load in a seconddirection. The active isolator assembly may include a single actuatorthat is coaxially aligned with a sensor. The sensor and actuator can beconnected to a controller which together provide active isolation of theload. The passive isolator assembly may include a pendulum that iscoupled to a dashpot. Providing a system with just one actuatorsignificantly reduces the cost of the vibration isolator with respect toisolators of the prior art.

Referring to the drawings more particularly by reference numbers, FIG. 1shows an embodiment of a table assembly 10 of the present invention. Theassembly 10 may include a platform 12 that is supported by a pluralityof legs 14. The platform 12 may have a honeycomb construction andinclude a plurality of mounting holes 16 which allow items such asoptical mounts to be attached to the table 10. As an alternateembodiment, the platform 12 may be constructed from a slab of granite.

The legs 14 may be interconnected by beams 18. The legs 14 extend from aplurality of feet 20. The feet 20 are in contact with a surface 22 suchas a floor of a building structure.

As shown in FIG. 2, each foot 20 may include a number of cleats 24 thatextend from a plate 26. The cleats 24 may penetrate a carpet 28 andsecure the table 10 to the floor. The cleats 24 assist in mechanicallyconnecting the table 10 to a solid floor located beneath the carpet.

Referring to FIG. 1, the table assembly 10 may include one or morevibration isolators 30. The isolators 30 are typically mounted to thebeams 18 of the table 10, or alternatively mounted in the table legs 14.The floor may undergo a vibrational movement that creates a varyingdisplacement of the surface 22. The isolators 30 isolate a load such asthe platform 12 from the varying displacements of the surface 22.

The table assembly 10 may further include a controller 32 which controlsthe vibration isolators 30. The controller 32 may control all threeisolators 30. Although three isolators 30 are shown and described, it isto be understood that four or any other combination of isolators 30 maybe employed in the present invention.

FIG. 3 shows an embodiment of a vibration isolator 30. The isolator 30may have an outer housing 32 that is mounted to a mounting surface suchas a beam 18 by fasteners 34. The housing 32 may include a lower section35 that is attached to an upper section 36 by fasteners 38. The isolator30 may include a post 40 that is attached to the lower section 35 of thehousing 32 by a fastener 42. The isolator 30 may also include a topplate 44 that supports the platform 12. When the table assembly 10 istransported, the top plate 44 and platform 12 may be secured by alocking plate 46 and fasteners 47 that screw into the plate 44 and thehousing 32.

The isolator 30 may include an active isolator assembly 48 and a passiveisolator assembly 50 that isolate the top plate 44 from the housing 32.The active isolator assembly 48 may isolate the plate 44 and platform 12in a first vertical direction. The passive isolator assembly 50 mayisolate the plate 44 and platform 12 in a second horizontal direction orplane.

The active isolator assembly 48 may include a piezoelectric actuator 54that is mounted to the post 40. The piezoelectric actuator 54 mayreceive a drive signal that either increases or decreases the height ofthe actuator 54 to isolate the plate 52 and platform 12 in the verticaldirection. The piezoelectric actuator 54 may be constructed from aplurality of piezoelectric elements which are maintained in compressionby a plurality of elastic elements such as bellville springs 60. Theactuator 54 also includes a push rod 56 connected to the piezoelectricelements by connecting blocks 58. The springs 60 are captured by a nut62 that is screwed onto the post 40.

The push rod 56 is attached to a cup 64 which houses a sensor 66. Thesensor 66 may be a geophone which provides an electrical output signalthat is a function of the motion of the actuator push rod 56.

The isolator 30 may include a filter assembly 70 that is coupled to theactive isolator assembly 48 and the passive isolator assembly 50. Thefilter assembly 70 may include an elastomer 72 that is attached to acoupler plate 74 and a plug 76 which is screwed into the cup 64. Thefilter assembly 70 filters out relatively high frequency vibrationsintroduced to the isolator 30 so that high frequency components are nottransferred from the floor 22 to the plate 44 and platform 12. Thisreduces the requirements for active system bandwidth.

FIG. 4 shows an embodiment of a filter assembly 70′ which has a resonantfrequency that remains relatively constant for a predetermined range offorces that may be applied to the assembly 70. The assembly 70′ mayinclude a profiled elastomer 72′ that is located within a profiledcavity 78 of the coupler plate 74. The profiles of the elastomer and thecavity are chosen so that, as load increases, the elastomer is pressedagainst the cavity walls, thereby increasing the stiffness which allowsfor relatively constant natural frequency. By way of example, a conicalshaped elastomer and cavity are chosen for the embodiment shown in FIG.4.

Referring to FIG. 3, the sensor 66 has a center axis that is coaxialwith a center axis of the actuator 54. Additionally, the center axes ofthe sensor 66 and actuator 44 may be coaxial with a center axis of thefilter assembly 70. The coaxial relationship between the actuator 54 andsensor 66 allow the sensor 66 to sense axial translational movement withminimal bending movements.

The passive isolator assembly 50 may include a plurality of cables orother tension members 80 that extend along an inner channel 81 of a tube82. The tube 82 is in contact with the top plate 44. The bottom ends ofthe cables 80 each have knobs 84 that are captured by an end plate 86.The end plate 86 is attached to the tube 82. The top end of the cables80 have knobs 88 that are captured by cable plugs 90 which are screwedinto the coupler plate 74. The cables 80 create a pendulum assemblywhich allows the top plate 44 and tube 80 to translate horizontallyabout the post 40.

The lower housing section 35 may include a reservoir 91 that is filledwith a fluid 92 such as oil. A portion of the tube 82 extends into thereservoir 91. The fluid filled reservoir 91 creates a dashpot that dampshorizontal movement of the plate 44.

FIG. 5 shows a schematic of the active 48 and passive 50 isolatorassemblies. The plate 44 is coupled to the coupler plate 74, sensor 66and actuator 54 by the tube 82 and cables 80. Flexing of the cables 80between the knobs 84 and 88 allows horizontal motion of the passiveisolator assembly 50. The passive isolator assembly 50 allows relativehorizontal movement between the plate 44 and the floor 22 as indicatedby the arrow 94. The passive assembly 50 also damps the movement withthe dashpot reservoir 91.

The actuator 54 varies in height to compensate for movement of the floor22 in the vertical direction as indicated by the arrow 96. The activeisolator assembly 48 prevents or reduces movement of the floor 22 frombeing transferred into the plate 44.

Referring to FIG. 3, during operation of the isolator 30, the top plate44 and platform 12 may move relative to the floor 22. It may bedesirable to move the top plate 44 and platform 12 back to a referenceposition.

The isolator 30 may have a docking assembly 100 that moves and securesthe plate 44 and platform 12 to the reference position. The dockingassembly 100 may include a pin 102 that is inserted into an aperture 104of the plate 52. Both the pin 102 and the aperture 104 may have lead inchamfer surfaces 106 and 108, respectively, which induce a movement ofthe plate 52 so that a center axis of the aperture 104 is aligned with acenter axis of the pin 102. The center axis of the pin 102 provides areference point for the plate 52 and platform 12.

The pin 102 may include a sleeve 110 that is attached to an output shaft112 of an actuator 114. The actuator 114 may be a linear stepper motor.The actuator 114 is attached to the housing 32. The actuator 114 canmove the pin 102 into and out of the aperture 104. During isolation, thepin 102 is pulled out of the aperture 104 to allow relative horizontalmovement between the plate 44 and the floor 22. The pin 102 can be movedback into the aperture 104 to align the plate 44 and secure the platform12.

FIG. 6 shows a schematic of an embodiment of the controller 32 thatcontrols the vibration isolators 30. The controller 32 may include aprocessor 120 that is connected to a memory device 122 by a bus 124. Theprocessor 120 may be a digital signal processor (DSP), the memory devicemay be non-volatile random access memory such as “flash” memory. Theprocessor 120 may perform software routines in accordance withinstructions and data stored in the memory device 122.

The controller 32 may include an amplifier 128 and an analog to digital(A/D) converter 130 that are connected to the sensor 66 and the bus 124.The sensor 66 generates an output signal that is a function of themotion of the actuator push rod 56 shown in FIG. 3. The amplifier 128amplifies, and may integrate and/or filter, the output signal of thesensor 66. The amplified signal is converted into a digital sequence bythe A/D 130 and provided to the processor 120.

The controller 32 may also include a digital to analog (D/A) converter132 and an amplifier 134 that are connected to the actuator 54 and bus124. The processor 120 provides digital sequences that are converted toan analog signal by the D/A 132. The output of the D/A 132 is amplifiedand provided to the actuator 54 shown in FIG. 3, to cause a contractionor expansion of the piezoelectric.

The stepper motor 114 may also be coupled to the bus 124 by a drivercircuit 135. The processor 120 may provide commands to actuate the motor114 and move the pin 102 shown in FIG. 3 in and out of the aperture 104.Although not shown, the processor 120 may be connected to A/Dconverters, D/A converters and amplifiers for each isolator of amultiple isolator table assembly. The control system may have a singleinput single output architecture or a multiple input multiple outputarchitecture between the processor and the isolators.

The controller 32 may include an input/output (I/O) port 136 that isconnected to the bus 124. A computer 138 can be connected to thecontroller 32 through the I/O port 136 to store or read information inthe memory device 122. By way of example, the processor 120 typicallyprovides output to the actuator 54 in accordance with a software routinethat utilizes a gain value and a transfer function. The gain andtransfer function can be stored in the memory device 122 through the I/Oport 136.

A number of different transfer functions can be provided on a storagemedium such as a floppy or optical disk 140 that is loaded into thecomputer 138. The disk 140 may also contain a software routine whichallows the operator to select one transfer function from a list ofdifferent transfer functions. Different transfer functions may be storedin memory 122 and selected by the operator using the computer 138 andthe I/O port 136. Different transfer functions may provide differenttransient response times for the isolators 30. The selected transferfunction is then stored in the memory device 122 through the I/O port136. The software on the disk 140 may also allow the operator to selecta gain value that is used to compute the output signal provided to theactuator 54. The system thus allows the user to select the gain andtransient response time of the isolators 30.

FIG. 7 shows a flowchart of a routine performed by the processor 120.When the system is initially powered up the processor performs aninitialization routine to undock the docking assembly, provide systemidentification and DC offset correction in process block 150. The DCoffset correction may include reading a DC level from the signalgenerated by the sensors. The DC level can be stored and then latersubtracted from the output signals of the sensors during operation tonormalize the signals.

After initialization, the process continues to process block 152 to readthe output signals of the sensors. The process then determines whetherto perform a docking routine in block 154. In block 156 the saturationvalues are checked and updated.

The output signals for the actuators are calculated in block 158. Thecalculations utilize the transfer function and gain value stored in thememory device. In block 160 the output signals are provided to the D/Aconverter to actuate the piezoelectric devices. The process then returnsto block 152 and repeats the routine.

While certain exemplary embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative of and not restrictive on the broad invention, andthat this invention not be limited to the specific constructions andarrangements shown and described, since various other modifications mayoccur to those ordinarily skilled in the art.

What is claimed is:
 1. A vibration isolator which isolates a load thatis separated from a floor, comprising: an actuator that is coupled tothe load and the floor and which has a variable height; a sensor thatsenses a vibrational movement of a point between the load and the floor;a memory that stores a plurality of different transfer functions forsaid actuator; an input device that allows an operator to select one ofthe transfer functions; a controller which is coupled to said actuatorand said sensor and which provides an output to vary the height of saidactuator in response to a feedback signal from said sensor to damp thevibrational movement in a transient response time, said output being afunction of a transfer function that is selected from the plurality ofdifferent transfer functions that each create a different transientresponse time.
 2. The vibration isolator of claim 1, further comprisinga passive isolator assembly that passively isolates the load.
 3. Thevibration isolator of claim 2, wherein said passive isolator assemblyincludes a pendulum assembly.
 4. The vibration isolator of claim 3,wherein said pendulum assembly includes a cable that is coupled to theload.
 5. The vibration isolator of claim 3, wherein said passiveisolator assembly includes a dashpot that is coupled to said pendulumassembly and the floor.
 6. The vibration isolator of claim 1, furthercomprising a docking assembly that secures the load relative to thefloor.
 7. The vibration isolator of claim 6, wherein said dockingassembly includes a pin that can be inserted into an aperture of a platethat supports the load.